Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 130547

Area Forecast Discussion
National Weather Service Bismarck ND
1247 AM CDT Sun Aug 13 2017

Issued at 1245 AM CDT Sun Aug 13 2017

H5 low over the forecast area with a wave circulation evident in
the radar data near Bismarck. A large area of showers was moving
through Logan, McIntosh, Dickey and laMoure counties to the
northeast. Another large area of rain was in the Mandan area and
this was shrinking in coverage and decreasing in intensity. Timed
southeast rain out of the area by 8 AM and dissipated the rain
around mandan by that time as well.

Concern then goes to fog, especially south, where some places had
three inches of rain. With light wind situation is conducive to
fog forming.

UPDATE Issued at 858 PM CDT Sat Aug 12 2017

Now seeing the short wave circulation in the radar reflectivity
and this should track southeast with time tonight. Updated the
POPs and QPF with the latest HRRR model run and also averaged the
QPF with the HRRR. Will see more rain across south central North
Dakota tonight. The latest CAM models, especially the RAP, bring
in fog over more of the south central. With the recent rains
extended the areas of tonight further east, but did not go to the
James river valley.

UPDATE Issued at 710 PM CDT Sat Aug 12 2017

Focused on the south central for heavy rain with the
thunderstorms this evening. generally increased POPs to likely
across this area.

UPDATE Issued at 446 PM CDT Sat Aug 12 2017

Quick update for the band of thunderstorms from Beach to Hazen
to south of minot. This area of thunderstorms has been producing
heavy rain. Do not expect flash flooding but getting some reports
of standing water on roads, along I-94 near Medora for example.


.SHORT TERM...(This evening through Sunday)
Issued at 248 PM CDT Sat Aug 12 2017

Latest GOES16 water vapor imagery loop shows a mid level upper
low circulating over northwestern ND, soon to transition south as
a stronger shortwave rotates and into southwest/south central ND
this evening. The mid/upper low slowly meanders into the southern
James River Valley after midnight. Areas of fog 05z-15z Sunday for
southwest and south central ND has been added to the gridded
forecast per HRRR/RAP13 Surface Visibility Forecast.

For this afternoon and evening, per water vapor imagery, our
attention is directed toward a pair of 700mb-500mb shortwaves
noted over Dawson and Custer Counties in eastern Montana. The
GFS/RAP13 have both initialized this very well with the current
location, and begins pushing these shortwaves into southwestern
ND 21z-00z, then into far south central 03z-06z, and exiting the
southern James River Valley 12z-15z Sunday. Large scale ascent
increases this afternoon southwest and far south central in
response to the shortwave aloft and the left exit region of a 60kt
300mb jet streak scooting through southeastern MT/southwestern
ND. A cold pocket of -16C also aiding in destabilization. Air
parcels will encounter moderate instability with mixed layer CAPE
between 1000-2000 J/kg, Effective Bulk Shear values of 40kt, and
mid level lapse rates around 7.5C/km. With that said, will
continue with previous forecasts and maintain a mention of severe
thunderstorms in far southwest and into far south central ND
through early this evening. This is also in line with the Marginal
Severe Thunderstorm Risk per SPC. Main threats of large hail and
damaging winds continue. Localized heavy rainfall (1 to 2 inches)
per WPC in a short amount of time with any thunderstorm remains
valid as well.

The Simulated High Resolution Composite Reflectivities in decent
agreement with developing pockets of showers/thunderstorms from
Williston south to Bowman, which is in line with the current
Regional Radar. The Non-Supercell Composite Index is between 1
and 2 over northwest ND. Will need to monitor the low level lapse
rates and surface vorticity for any potential landspouts that
could develop within this area.

Scattered showers and thunderstorms continue through the evening,
then shift away from southwest ND towards midnight. As mentioned
above, concur with fog southwest and south central given the
moisture, and crossover temperatures being met later tonight per
BUFKIT soundings.

.LONG TERM...(Sunday night through Saturday)
Issued at 248 PM CDT Sat Aug 12 2017

A mid level transitory shortwave ridge shifts into eastern MT and
western ND Sunday, behind the departing upper low. Increasing
sunshine west Sunday morning, with clouds decreasing in the
afternoon in the central. Lingering precipitation over the James
River Valley Sunday morning, diminishes through 18z Sunday before
ending. Highs in the 70s.

The next in a series of shortwaves moves into eastern MT and
western ND Monday with a chance for showers and thunderstorms.
Additional shortwaves traverse through a southwest flow aloft
Monday night through Tuesday night affecting western and central
ND with showers and thunderstorms. A break on Wednesday with
another shortwave slated for Thursday/Thursday night. Highs in the
upper 70s to lower 80s Monday through Saturday.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1245 AM CDT Sun Aug 13 2017

Rain showers from the KBIS to the KJMS area will be dissipating
by 13/1200Z. Excessive low level moisture from three inches of
rain that fell in spots Saturday and light wind will support fog
forming, especially south, KDIK-KBIS-KJMS before daybreak Sunday.
Areas of IFR ceilings and visibilities are possible. For now have
included BR as a tempo possibility.




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